Up to half of all women going through menopause report significant sleep disturbance. A number of factors contribute to these sleep problems, with hormonal imbalance and hot flashes being the most important. Estrogen replacement therapy can alleviate these symptoms, yet side effects and contraindications make the use of this hormone replacement therapy (HRT) problematic in many women. As such, alternatives to traditional HRT are needed. Previous work in our lab has indicated that not only low levels of sex steroids but also the marked increase of gonadotropins observed during the menopause transition may play an important role in disturbed sleep experienced by peri- and postmenopausal women. In particular, our studies have shown that elevated levels of luteinizing hormone (LH) or a high ratio of LH-to-estradiol were associated with low sleep- efficiency in postmenopausal women. Hormonal imbalance also induces changes in the thermoregulatory system. The result is hot flashes and sweats, which can adversely affect night-time sleep quality The proposed study will test the hypothesis that exogenous melatonin decreases LH levels and in so doing, increases sleep quality. Furthermore, we hypothesize that melatonin will reduce severity and number of hot flashes by virtue of its temperature-lowering effect. As a consequence, the number of awakenings due to nocturnal hot flashes and night sweats will be reduced, leading to improved sleep quality. To test these hypotheses, twelve symptomatic peri- or postmenopausal women between the ages of 45-55 will ingest a daily dose of 3 mg melatonin or placebo every evening at bedtime over a period of 14 days. Each subject will undergo both conditions. At the end of each treatment session, subjects will spend two consecutive nights in the sleep laboratory. Polysomnographic sleep variables and core body temperature will be recorded continuously on both nights. Hot flashes will be objectively identified by measuring distal skin temperature and proximal skin resistance. Over-night urine samples will be collected to assess LH levels. Sleep parameters, temperature data, number of hot flashes and LH levels will be compared across active and control condition. The current project is an important first step to identify and assess a promising alternative for sleep disturbances in menopause.